The cornea: clarity, nerves and healing
- Anatomy and physiology
The cornea is the clear window at the front of the eye and its strongest lens. It has no vessels, many nerves, and an inner cell layer that keeps it clear.
See it in 3D: Cornea · Sclera · V1 ophthalmic
What it is
The cornea is a transparent, avascular dome about half a millimetre thick at its centre. It provides about two thirds of the eye's focusing power. Its clarity depends on the regular spacing of collagen fibres in the stroma and on the endothelium, which pumps water out. It is one of the most densely innervated tissues of the body, so even small injuries hurt.
Clinical anatomy
- Epithelium: several layers of cells that renew from stem cells at the limbus (the corneal edge).
- Bowman layer: an acellular layer under the epithelium; it does not regenerate and scars when damaged.
- Stroma: about nine tenths of the thickness, made of regularly arranged collagen lamellae.
- Descemet membrane: the basement membrane of the endothelium.
- Endothelium: a single layer of cells that pumps fluid out of the stroma; in humans it does not regenerate.
Physiology
- It refracts light: the air-tear-cornea interface is the strongest lens of the eye.
- It is nourished by the tears, the aqueous humour and the limbal vessels, not by its own vessels.
- Its sensory nerves come from the ophthalmic division of the trigeminal nerve and drive the corneal (blink) reflex.
Clinical correlation
- A pure epithelial abrasion heals within one to three days without a scar; injuries deeper than Bowman layer leave an opacity.
- Loss of endothelial cells (Fuchs dystrophy, surgery, trauma) lets the cornea swell and cloud.
- Destruction of the limbal stem cells (chemical burns) leaves a cornea that cannot heal its surface.
- The corneal reflex tests the trigeminal nerve (afferent) and the facial nerve (efferent).
Next step / Initial management
- Abrasion: topical antibiotic, analgesia and review if not healed in 24 to 48 hours.
- Corneal opacity, infiltrate or ulcer: same-day ophthalmology.
- Herpes zoster on the tip of the nose (nasociliary branch): high risk of eye involvement; refer to ophthalmology.
- Progressive irregular astigmatism in a young person: refer for keratoconus assessment (corneal cross-linking can halt it).
Test yourself
Think of the answer, then tap the question to see it.
Which corneal layer keeps the cornea clear by pumping water out?
The endothelium, which does not regenerate in humans.
Where are the stem cells that renew the corneal epithelium?
At the limbus, the junction of cornea and sclera.
Why does herpes zoster on the tip of the nose predict eye involvement?
Because the nasociliary nerve supplies both the tip of the nose and the cornea.
Elsewhere in DurgiPedia
Connections
See it in 3D3
The structures of Durgical's 3D anatomy where it is found.
Educational content; not a clinical guideline and no substitute for assessment by a health professional. For sudden visual loss, severe eye pain, a chemical burn or an eye injury, go to an emergency department at once.
Sources: Anatomy, Head and Neck, Eye Cornea (StatPearls Publishing (NCBI Bookshelf), 2023); Corneal Abrasion (StatPearls Publishing (NCBI Bookshelf), 2024).
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Representative model, for educational purposes only.